Magneto-mechanical resonators (MMRs), also referred to as magnetoelastic (MEL) resonators, are well known and have been used in retail security applications for decades. In addition, MEL resonators are also suitable for buried infrastructure due to their low cost, low profile and flexible components. They can be configured as stand-alone markers or physically attached to an underground pipe or utility. They can be used to identify a buried asset and its location accurately. For example, see US 2012/068823; US 2012/0325359; and US 2013/0099790, each of which is incorporated herein by reference in its entirety.
However, the detection range and frequency stability of such conventional MEL resonators can be limited.